(i) Field of the Invention
This invention relates to a method and apparatus for applying liquid settable material to board products and particularly, but not exclusively, is concerned with impregnation of corrugated cardboard products with wax.
(II) Prior Art
Corrugated cardboard boxes intended for certain uses are customarily impregnated with wax to increase the strength of the boxes and to give some measure of water resistance. When impregnation of this kind is effected it is desirable that the wax should impregnate not only outer surfaces of the box but also the surfaces of the inner layer of corrugated board material. The boxes may be impregnated in their partly assembled condition, that is when the box blanks have been glued but not erected or they may be impregnated by first impregnating the board from which the box blanks are to be formed. In the latter case difficulties may be experienced in forming secure joints between parts of the box blanks because the waxed board does not take adhesive as well as unwaxed board. This difficulty can usually be overcome by the use of special glues but this may not always be practicable and is generally inconvenient and relatively expensive. The difficulty can also be avoided to some extent by impregnating the board by a known method involving passing the wax only between the outer board layers and down the tubular interstices in the board provided between the outer layers and the inner corrugated layer so that the interior surfaces of the corrugated board are impregnated but not the outer surfaces. This does, however, require very careful control of the impregnating operation since seepage of wax to the outer surfaces of the board can occur. Furthermore, this method is not suitable for relatively thin material where it will normally be impossible to prevent seepage to the outer surfaces no matter how careful the control be of the impregnating process.
If the blanks for the boxes are impregnated after formation of glued joints the above difficulties do not, of course, arise. However, impregnation of glued but not erected blanks has been found to be difficult because of the relatively complex shape of the blanks in this condition. It has been found difficult to thoroughly impregnate the inner parts of the blank material and even where good impregnation has occurred there is a tendency for the wax to coalesce in the ducts formed by the board interstices thus causing waste of wax and also frequently presently an unattractive appearance.